We utilized an Adjustable Ring-Mode (ARM) laser to achieve an almost fully equiaxed microstructure in powder bed Fusion-laser beam Scalmalloy®. ARM laser-built specimens exhibited over 90% fine-grained material, while circular laser-built specimens yielded less than 50% fine-grained material, using the same laser power, speed, and hatch spacing. To gain insights into these interesting results, we employed a Cellular Automata (CA) solidification simulation, incorporating the nucleation role of L12 Al3(ScxZr1-x) precipitates through a particle-based nucleation model. The simulation was coupled with the corresponding temperature field derived from finite difference analyses of the circular and ARM laser beams. The simulation results revealed a significantly thicker precipitation zone (equiaxed grains) under the ARM laser compared to the circular beam, primarily attributed to reduced temperature and cooling rates. The excellent correlation between simulation and experimental results demonstrates promising potential for the predictive application of the developed model. It can be effectively utilized to optimize heat source modulation and process parameters, thereby enabling the adaptation of microstructure and mechanical properties.